Condensed Consolidated Statement of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Distributions in Excess of Accumulated Earnings [Member]	Accumulated Other Comprehensive Loss, Net [Member]	Noncontrolling Interest [Member]
Issuance of common stock under:
Cumulative effect upon adoption of ASU | ASU 2016-01 [Member]				$ 2,234
Cumulative effect upon adoption of ASU | ASU 2017-05 [Member]				119,651
Balance at period beginning at Dec. 31, 2017	$ 6,396,825	$ 7	$ 7,129,571	(833,726)	$ (18,446)	$ 119,419
Balances (in shares) at Dec. 31, 2017		66,054
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	96,639			90,918		5,721
Reversal of unrealized losses upon the sale of marketable debt securities	(1)				(1)	0
Change in fair value of derivatives and amortization of swap settlements	6,254				6,046	208
Change in fair value of marketable debt securities, net	(77)				(74)	(3)
Issuance of common stock under:
Stock option and restricted stock plans, net	1,222	$ 0	1,222
Stock option and restricted stock plans, net (in shares)		7
Sale of common stock, net	(67)		(67)
Equity based compensation costs	2,530		2,253			277
Retirement of common stock, net	(3,774)	$ 0	(3,774)
Retirement of common stock, net (in shares)		(17)
Changes in the redemption value of redeemable noncontrolling interest	(1,953)		(1,957)			4
Distributions to noncontrolling interest	(6,297)					(6,297)
Common stock dividends	(122,850)			(122,850)
Balance at period end at Mar. 31, 2018	6,492,159	$ 7	7,127,248	(743,773)	(14,709)	123,386
Balances (in shares) at Mar. 31, 2018		66,044
Issuance of common stock under:
Cumulative effect upon adoption of ASU	181				175	6
Cumulative effect upon adoption of ASU | ASU 2016-01 [Member]	0				(2,234)
Cumulative effect upon adoption of ASU | ASU 2017-05 [Member]	123,708					4,057
Balance at period beginning at Dec. 31, 2018	6,393,844	$ 7	7,093,079	(812,796)	(13,217)	126,771
Balances (in shares) at Dec. 31, 2018		65,890
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	125,505			118,858		6,647
Reversal of unrealized losses upon the sale of marketable debt securities	33				32	1
Change in fair value of derivatives and amortization of swap settlements	(1,993)				(1,926)	(67)
Change in fair value of marketable debt securities, net	123				119	4
Issuance of common stock under:
Stock option and restricted stock plans, net	3,204	$ 0	3,204
Stock option and restricted stock plans, net (in shares)		51
Sale of common stock, net	(20)		(20)
Equity based compensation costs	2,600		2,301			299
Retirement of common stock, net	(56,989)	$ 0	(56,989)
Retirement of common stock, net (in shares)		(234)
Changes in the redemption value of redeemable noncontrolling interest	(1,767)		(3,027)			1,260
Distributions to noncontrolling interest	(7,164)					(7,164)
Redemptions of noncontrolling interest	(12,213)		(10,394)			(1,819)
Redemptions of noncontrolling interest (in shares)		9
Common stock dividends	(128,149)			(128,149)
Balance at period end at Mar. 31, 2019	$ 6,317,195	$ 7	$ 7,028,154	$ (822,087)	$ (14,817)	$ 125,938
Balances (in shares) at Mar. 31, 2019		65,716